In general, in automatic processing apparatus of photosensitive printing plate, as a measure of managing the sensitivity of a developer, there is employed a replenishment mode with time of developer replenisher, in which a developer replenisher is replenished with time in a development tank where a developer is stored, and a plate area of a lithographic printing plate to be treated is measured, thereby replenishing the developer replenisher in an amount corresponding to the measured value (hereinafter referred to as “area/elapse standard replenishment mode”)
However, in such an area/elapse standard replenishment mode, there was involved a problem that a plate area measurement device of lithographic printing plate is required in a development treatment section of an automatic processing apparatus, resulting in complication of the structure and high costs. Also, it is difficult to discriminate whether a photosensitive surface of the lithographic printing plate is a single side or both sides (hereinafter referred to as “single side/both sides”) and the kind of plate (plates having a different coating amount of photosensitive layer, etc.). For those reasons, there was a problem that when the replenishment amount of the developer replenisher as required varies according to changes in the plate area, single side/both sides and kind of plate of the lithographic printing plate, it is difficult to properly carry out replenishment of the developer replenisher.
Thus, as a method of replenishing a developer replenisher of an automatic processing apparatus for photosensitive lithographic printing plate, a mode in which an electric conductivity of the developer is measured, the measured value is compared with an electric conductivity value to exhibit the optimal sensitivity as experimentally determined in advance (hereinafter referred to as “proper electric conductivity value”), and when the measured value is lower than the proper electric conductivity value, the developer replenisher is replenished (this mode being hereinafter referred to as “electric conductivity-standard replenishment mode”) is hitherto known as described in, for example, Japanese Patent No. 2,516,022 (JP-A-64-21451). In such an electric conductivity-standard replenishment mode, even when the plate area, single side/both sides and kind of plate of the lithographic printing plate to be treated change, it is possible to conduct replenishment of a proper amount of the developer replenisher and to properly keep the sensitivity of the developer.
However, there is an empirical fact that the developer fatigued with time only by carbon dioxide gas and the developer fatigued only by the plate treatment are different from each other in the proper electric conductivity value (silicate based treating agent/elapsing fatigue (fatigue by carbon dioxide gas)-replenishment recovery time: 65 mS/cm, fatigue by treatment-replenishment recovery time: 55 mS/cm, non-silicate based treating agent/elapsing fatigue-replenishment recovery time: 56 mS/cm, fatigue by treatment-replenishment recovery time: 39 mS/cm). For that reason, in the foregoing electric conductivity-standard replenishment mode, in the case where the treatment frequency, for example, the treatment amount per day is different from the expected value, a ratio of the actual elapsing replenishment amount to the treatment replenishment amount is also different from the expect value. Accordingly, the proper electric conductivity value of the developer calculated from the respective proper electric conductivities changes and becomes different from the proper electric conductivity value as set up in advance, resulting in a problem that the sensitivity of the developer cannot be kept properly.
On the other hand, JP-A-9-96910 proposes an automatic processing apparatus in which a replenishment time interval is measured, an elapsing replenishment amount that is considered necessary within the time interval is determined, a value obtained by reducing this elapsing replenishment amount from a replenishment amount per time is regarded as a treatment replenishment amount, thereby determining the treatment replenishment amount and the elapsing replenishment amount, respectively, and a proportion of the treatment replenishment amount to the elapsing replenishment amount as obtained is calculated, thereby correcting a target electric conductivity value. According to this measure, even when the plate area, single side/both sides and kind of plate of the lithographic printing plate to be treated change, by estimating a proportion of the treatment replenishment amount to the elapsing replenishment amount, it is possible to precisely calculate a proper target electric conductivity value.